ES2 Metamorphic Rocks - Metamorphic Microstructures #5
Relict igneous texture.
This is a greenschist-facies metagabbro. The texture of the original gabbro is still detectable, but the rock is entirely made up of low-grade metamorphic minerals. The plagioclase laths are now albite in composition, and the igneous pyroxene has been transformed into aggregates of pale dirty-green actinolite and chlorite. In the lower photograph the actinolite shows yellow-orange interference colours and jagged, fibrous terminations, and the chlorite is almost isotropic.
PPL and crossed polars. Field of view is 2.5 mm across.
Greenschist facies metabasite, Sample 69-266
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DJW - August 1997